Palynology of Holocene Lake Baikal sediments Palynology of Holocene Lake Baikal sediments Ali£©nor Labes

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  • Palynology of Holocene Lake Baikal sediments

    Aliénor Labes Adriano Mazzini, Grigorii G. Akhmanov, and Wolfram M. Kürschner

  • Baikal is the largest freshwater

    lake by volume in the world,

    containing 23% of the world's

    fresh surface water. The Lake

    fills the central depression of a

    25 million years old continental

    rift zone and provides a large

    variety of active geological

    features. Morphologically the

    lake comprises three basinal

    areas:

    1 & 2. - The southern and

    central depressions divided by

    a depositional high resulting by

    the deltas of the Buguldeyka

    and Selenga Rivers.

    During the TTR6 Class@Baikal expedition (2019) a

    multidisciplinary survey completed set of geophysical and

    sampling profiles intersecting

    1) The Gydratny fault in the central basin of the lake and

    2) Several piercements structures in the southern and central basins.

    TTR-BL19 Class@Baikal expedition

    Khlystov et al, 2019, MPG

    3- The central and northern

    depressions separated by a SW-

    NE oriented tectonic high

    comprising terrestrial and

    subaqueous segments. Red line shows the areas investigated during the TTR-BL19 cruise.

    Central basin

    Gydratny fault

    Southern basin

  • This study shows the preliminary results of palynological studies on sediments

    recovered from two distinct areas where different geological phenomena

    occurred.

    1. Central Basin- Gydratny fault region

    Profiles through the fault revealed the presence of turbidites and «woody

    turbidites». The source area and dating of these units remain unknown.

    2. Piercements in central and southern basin

    Several mud volcanoes and putative mud volcanoes have been cored. The age of

    the erupted sediments is unknown and a proxy to distinguish mud breccia

    sediments has not been found yet.

    Purpose of this study

  • Candidate sources for input of sedimentary and wood deposits include:

    1.Selena river delta through Kukuy canyon

    2.Anga river delta

    3.Olkhon Gates

    4.Khuray region

    5.Landslides from Northern shore

    Seismic and sampling profiles colleted through the Gydratny fault. Sampling stations are marked by yellow dots, and the red dots represent identified woody turbidites. Wood deposits most abundant on F and D lines.

    Gydratny fault woody turbidites: setting

    Olkhon Gates

    Gydratny fault

  • CORES OBSERVATIONS

    • Decreasing thickness of the deposits towards the eastern side of the lake

    • Multiple events identified and can be correlated

    • Similar observations can be done for other profiles

    Gydratny fault woody turbidites: observations

    x

    core BL19-424

    Example of core with thick woody deposits studied for

    palynology Example of cores collected along profile F with

    identified woody turbidites (red areas)

    Pinus

    Picea

    Pine

    Spruce

    Grains reveal age ranging between 500- 2000 years old.

    PALYNOLOGY OBSERVATIONS

    pollen types dominated by recent species

    W E

  • OBSERVATIOSN SUMMARY

    • Young age of dated woody turbidites (500-200 yrs) correleates them with recenly triggered events

    • Woody deposits thinning towards the east suggest a source area from the west- north-west

    • Buoyancy of the wood suggests that these deposits were transported to the lake floor with a significant amount terrigenous material

    PROPOSED SCENARIO

    • Multiple gravitative mass movements from onshore landslides in the northern coast are the source of large amounts of sediments and wood debris

    • The acceleration prompted by the steep slopes on the northern coast allowed transport of the slumped material over great distances ultimately reaching the center of the central lake Baikal basin

    Gydratny fault woody turbidites: scenario

    Example of onshore landslide

  • Challenging identification MVs in Lake Baikal: hard to prove that extrusion of sediments occured at the lake floor:

    • Typical presence of gas hydrates that once dissociating homogenize the sediments

    • Lack of classic mud breccis deposits (I.e. NO clasts)

    • Absence of microfossils except for diatoms

    • As Baikalian MVs are shallow rooted diatoms assemblages have limited variations at shallow depths

    Potential proxies used to study sediments of putative Baikalian mud volcanoes:

    • Study or semi-lithified clasts (petrography/grainsize) extracted from cored sediments

    • Tomography of the cores to observe chaotic structure

    • Palynological analysis of semilithified clasts, surrounding matrix and compared with surface sediments

    Mud volcanism in Baikal: Challenges

    Typical mud volcano (MVs) deposits

    • Consists of erupted mud breccia (i.e. fine grained matrix incorporating clast of the different lithologies brecciated throughout the MV conduit and expelled at the surface)

    • Dating can be done through micro- paleontological studies, petrography of the clasts, and the surrounding matrix

    Examples of mud breccia clasts from Mediterranean MVs and relative petrography and micropaleontology studies

    Semi-lithified clasts

    Tomography studies

    Palynology studies

  • Palynological analysis on inferred mud volcanoes was achieved in the following areas:

    • Elovsky area sampling line- located in the north part of lake Baikal southern basin and to the west from Selenga river delta

    • Malen’ky sampling area- located in the South basin of the lake Baikal on the proposal continue of the Gydratny fault at the south-west side of the Selenga river delta

    • Gorevoy Utes sampling area-Located in the eastern-central part of lake Baikal.

    Studies of putative mud volcanoes

    • These targeted structures are gas

    hydrate bearing

    • Sediments are highly disturberd after

    clathrates dissociation

    • So far it remain unknow if these can be

    classified as mud

    volcanoes

  • Clasts and matrix samples from the Gorevoy Utes sampling area were processed and analysed (core BL19-414):

    Betula Pinus

    Picea Larix

    Palinology of Gorevoy Utes: some results

    Preliminary palynology results from the surface sediments compared with the mud breccia matrix and the semi-lithified clasts show that:

    • The matrix and the upper sediments contain younger, better preserved and more abundant pollen grains

  • • Preliminary studies revealed that palynology is a useful tool to date Lake Baikal sediments

    • Wood turbidite deposits through the Gydratny fault, revealed to be correleated to young events (500-2000).

    • We propose a scenario where onshore ladndslides are the source for copiuos amounts of sediments and wood debries. These are transported and ultimately deposited at

    great distances from the shore.

    • Semi-lithified mud clasts from putative mud volcanoes reveal older assemblages when compared with the surrounding matrix and the surface sediments.

    • Additional palynology analysis will be conducted in further studies, and the dating of more samples from different core sections is planned.

    Conclusions

  • Thank you for your time!